DIAMOND BAR, Calif. - After a new neighbor moved in across the street from Betty Phillips, the block took on a distinctive odor.

"It was awful," she said. "I thought we had skunks."

Last month, Phillips discovered that the smell was coming from a different suburban nuisance - one that is increasingly finding its way into upscale enclaves around California and the rest of the nation.

Inside her new neighbor's $580,000, three-bedroom home, police found 1,886 marijuana plants with an estimated street value of up to $10 million.

A week earlier and a few miles across town, investigators discovered about 2,100 plants worth up to $12 million in a 3,000-square-foot, two-story home, which in January had sold for more than $800,000.

On Wednesday, two more pot-growing homes were found in Rowland Heights, a bedroom community a few miles west of Diamond Bar. The homes had a combined 1,800 plants worth up to $10 million, an investigator said.

Officials in San Diego also announced Wednesday that they had shut down a novel growing operation - 454 plants in a series of underground rooms accessible by elevator - in Santa Ysabel.

While the indoor marijuana farms in Diamond Bar weren't quite that creative, the discoveries shocked residents of this clean, quiet, suburban city of 58,000 people nestled in the hills about 25 miles east of Los Angeles.

But law enforcement officials say that the locals have simply discovered what many suburban families across North America have already learned: Large-scale pot growers want to be their neighbors.

The emerging trend should concern suburbanites, even if they believe that marijuana isn't a hard-core drug, the officials point out. Because wherever millions of dollars' worth of pot plants go, criminals and violence often follow.

Having such a criminal enterprise in a neighborhood setting is "fraught with potential danger," said Dan Simmons, an agent in the Drug Enforcement Administration's San Diego field office.

Wondering about your new neighbors? Here are some signs that law enforcement officials say can indicate a house is functioning as an indoor marijuana farm:

- Windows are perpetually covered and blinds are drawn. Police were tipped off to a Pomona growing operation recently after neighbors said they saw drywall covering the windows and doors.

- An unkempt lawn. The yard of a recently raided home in Diamond Bar had waist-high dandelions in it - the serious gardening was going on inside.

- A strong, skunk-like odor. One investigator said the heavy winds last month helped tip him to a growing operation in Chino Hills. One Diamond Bar home, however, had a special ventilation system installed to lower the odds of olfactory detection.

- Lack of activity around the home. Mail piles up and garbage cans rarely go to the curb.

- When the neighbors move in, they lack furniture and appliances.

- The new residents avoid contact with neighbors. "If you bring them cookies as a welcome present, don't expect to be invited in for coffee," said DEA Agent Gordon Taylor.

"In the past several years there has been a proliferation of indoor growers," he added. "If I could attribute that to anything, it would be the perceived ease with which you can grow marijuana in your own home."

The DEA said more than 400,000 plants were seized from so-called "grow houses" nationwide in the last year - a steep increase from the 270,000 plants discovered in 2005.

San Diego County has had several in addition to the one that recently came to light in Santa Ysabel.

DEA and Internal Revenue Service agents found more than 1,000 plants last year in two Oceanside homes owned by Bardia Rahimzadeh, who pleaded guilty last year to charges in connection with that case.

Brothers Christopher and Eric DeMatteis also pleaded guilty last year to charges in connection with 555 plants discovered in a house Eric owned in a gated Oceanside community.

In Florida, Georgia, New Hampshire and Washington state, law enforcement officials have found well-to-do residences that essentially have been gutted, rewired and turned into greenhouses with the purpose of using every square foot for marijuana production.

In the last nine months alone in California, law enforcement agencies have found 50 grow houses, almost all of them in new housing developments ranging from the Sacramento area to the Central Valley. Roughly 24,000 plants worth an estimated $90 million were seized and 16 people were arrested, said Gordon Taylor, a DEA agent based in Sacramento.

Law enforcement officials said they believe those houses are connected to a Vietnamese organized-crime outfit from the San Francisco area.

"Why are they picking these neighborhoods? One theory is that in these newer developments there is a relative anonymity. People don't really know their neighbors and (they are) less likely to have suspicions raised if someone is not there that often," Taylor said.

Almost all the Northern California homes were purchased using 100 percent financing, Taylor said. In fact, the homes were so heavily financed that there was nothing for the owners to forfeit to the government.

The trend appears to have originated in the Canadian province of British Columbia, Taylor said, where Asian organized crime groups are suspected of having thousands of growing operations. Their product, known as "B.C. Bud," is highly potent and can draw up to $5,000 a pound.

American growers apparently "have stolen a page from the B.C. Bud handbook," turning up first in Washington state and now California, Taylor said.

The intended market for the marijuana is not certain, he noted, but "we know that pot clubs generally like indoor-grown marijuana. It tends to be more potent than outdoor-grown marijuana. ... It wouldn't surprise me at all if some was destined for pot clubs."

Investigators said they are trying to determine if the growing operations discovered in recent weeks in the Los Angeles area are connected. They are also looking into whether the houses - all in communities with large Asian populations - are linked to the Northern California cases.

In the Diamond Bar houses - as in many other grow houses discovered in California - the marijuana was grown not in soil but hydroponically, in a nutrient solution. Intense growing lights were on around the clock. Electrical wiring was altered to bypass the utility meter boxes.

In essence, the growers were not only raising pot plants, they were stealing electricity.

Taylor said marijuana producers prefer growing indoors rather than in natural conditions because the crops can be harder to detect, the plant quality can be better controlled, and the crops can yield more in a year.

In the Diamond Bar homes, which were both recently purchased, holes were cut into walls and ceilings for electrical lines and growing lights. Days after the raid, silver reflective sheeting remained tacked up on the ceilings of some rooms in one of the houses. Thick tangles of electrical wiring were everywhere.

"There was no furniture, no clothing, no personal items" in either of the Diamond Bar houses, said Jim Whitten, a lieutenant with the Los Angeles County Sheriff's Department. "Every room except for the bathroom was (for) wall-to-wall marijuana growing."

Nevertheless, while some neighbors of the Diamond Bar homes said they were worried about possible retribution from associates of the arrested growers, others said the pot operations caused little concern.

"It's not like it's a crack house," said Bill Maher, a seven-year Diamond Bar resident who lives across the street from the house raided on March 21.

Neighbors of these homes have good reason to be concerned. Some homes with indoor pot-growing operations have suffered damage from fires, possibly because of substandard rewiring. In Oceanside earlier this year, firefighters arrived at a burning home and discovered hundreds of marijuana plants in a coverted garage.

The DEA's Taylor also pointed out that while many people don't consider marijuana to be a hard drug, it's serious business to the people who cultivate and distribute it.

"When you have organized crime groups where millions of dollars are at stake, it would not be unusual for there to be violence involved at some point," he said.